JP 2002-349364A describes a gas leak sensing device for an evaporation fuel purge system, which detects abnormality generated in components of the system such as fuel tank, canister, or piping.
The gas leak sensing device drives a purge pump to lower the pressure in the system in the state where the purge control valve is open and where a valve for a canister is closed. Then, the purge pump is stopped and the purge control valve is closed when a predetermined time is elapsed after the purge pump is stopped, such that the purge system is in the tightly closed state with negative pressure. Under this situation, when the pressure increasing speed in the purge system is relatively large, it is determined that there is an abnormality such as leak in the purge system. For example, if a crack is generated in a piping of the system, outside air flows into the purge system. When the pressure increasing speed in the purge system is relatively small, it assumes that the pressure increase is based on only evaporation of fuel in a fuel tank, and it is determined that the purge system is normal.
The gas leak sensing device is able to detect an abnormality such as leak in a passage between a fuel tank and a purge control valve. However, the gas leak sensing device is not able to detect an abnormality such as leak in a passage, for example, a hose which connects a purge control valve to an intake passage of an internal combustion engine.